A geohydrological survey also referred to as hydrogeological or groundwater survey, is an investigation of the hydrologic and geologic parameters at the subsurface level in a particular area. Hydrogeological maps may be formulated with the data gathered during such a study. It involves the detailed evaluation of the water-bearing levels of rocks and their capability for filtration. Moreover, the intrinsic ability of these rocks to either store or resist water is also assessed. The pressure, type and quality of the underground water is noted, delving into the intensity of the water flow through pores or fractures.
A hydrogeological survey is done to determine the underground water level. Hydrogeological surveying is conducted prior to drilling a borewell in order to ascertain the quality and quantity of water available at a particular location.
Hydrogeological surveys may be conducted on a large, medium or small scale depending upon the purpose of the procedure. Firstly, researched data from government and private agencies that are already available is assessed, followed by extensive field work as needed.
A small-scale survey (1:1,000,000-1:500,000) is done in areas that have never been investigated previously, to gather preliminary information of the hydrogeological condition. These comprise details regarding the ability of the rocks in the area to retain water and overall underground water quality. Medium-scale surveys ((1:200,000-1:100,000) are more elaborate, conducted to collate information for hydrogeological mapping. Water-bearing complexes are mapped and a specific study is conducted regarding the retentive capacity of the rocks in the region.
Large-scale hydrogeological surveys (1:50,000and greater) are mostly initiated in order to deal with precise issues at the stage of engineering and operational planning. Areas, where water collection can be done, are identified and underground water reserves are examined through this type of survey. Medium and large-scale surveys also require drilling procedures, evaluation of the composition of the underground water and its quantity along with a proper measure of its flow. Construction of wells and pumping tests may be performed to understand the hydrogeological condition thoroughly.
Surface Hydrological Surveying
The objective of a surface hydrological survey is to define flood magnitude for given return periods. As part of the hydrological survey, hydraulic calculations are made with the aim of establishing the levels and velocity of water flowing within a plot or site in question and coming up with a pre-design of a drainage system which can cope with possible flooding during the return periods considered.
Analyses are then carried out, to manage water flow within the plot or site which is the object of the assessment; calculations are made using basic available data and by using methods such as, the American Rational Method, Triangular Unit Hydrograph, Ven Te Chow and SCS.
Models are used based on the programs such as; ArcGIS, HEC-Ras, HEC-RAS 2D, and eventually HEC-HMS (SCS), by which maximum flow, the extent of the flood surface, and the resulting water levels and velocity on the area (topography), are calculated. Flood maps are generated for different return periods. The water surface can be identified by intersecting it with the MDT model.
Economic (mining) Geological Surveying
A geological survey is concerned with the methodical study of the subsurface for creation of geological maps. Several geological techniques are used for this purpose, including the conventional visual survey, studying of landforms, hand and machine driven bore holes, remote sensing systems like satellite imagery and aerial photography.
Numerous surveying techniques are used for geological surveys like laboratory test results, and modeling approaches to understand the characteristics of the earth. In the usual geological surveying, the primary information is concerning the study of rocks, their location, and the deformation and examination of the sedimentary layers. In addition, the soils, landscapes, rivers, and glaciers are examined. Usually the surveying tasks include:
- Geological mapping
- Structural mapping to indicate the location of the main rocks and the faults due to which they were placed there
- Surficial mapping for the location of soils
- Survey of topographic features
- Formation of topographic maps
- Survey to identify changes in landscapes, erosion patterns, and river channels
- Subsurface mapping by seismic surveys, ground penetrating radar, and electrical tomography
Economic geological Surveying focuses on earth materials that can be used for economic and/or industrial purposes. These materials include precious and base metals, non-metallic minerals and construction-grade stone. The techniques employed by other earth science disciplines (such as geochemistry, mineralogy, geophysics, petrology and structural geology) might all be used to understand, describe, and exploit an ore deposit.
Economic geological surveying may be of interest to other professions such as engineers, environmental scientists, and conservationists because of the far-reaching impact that extractive industries have on society, the economy, and the environment.
Petroleum Geological surveying
Petroleum Geological surveying: Petroleum geological surveying is the study of origin, occurrence, movement, accumulation, and exploration of hydrocarbon fuels. It refers to the specific set of geological disciplines that are applied to the search for hydrocarbons (oil exploration). Desk study, aerial survey, seismic survey, exploratory drilling, appraisal, development and production are steps to assess a designate field for oil or gas prone.
Environmental Geological Surveying
Environmental geological surveying, like hydrogeological surveying, is an applied science concerned with the practical application of the principles of geology in the solving of environmental problems created by man. It is a multidisciplinary field that is closely related to engineering geological and, to a lesser extent, to environmental geography. Each of these fields involves the study of the interaction of humans with the geologic environment, including the biosphere, the lithosphere, the hydrosphere, and to some extent the atmosphere. In other words, environmental geology is the application of geological information to solve conflicts, minimizing possible adverse environmental degradation or maximizing possible advantageous conditions resulting from the use of natural and modified environment. With an increasing world population and industrialization, the natural environment and resources are under high strain which puts them at the forefront of world issues. Environmental geology is on the rise with these issues as solutions are found by utilizing it.
Engineering Geological/ Geo-technical Surveying
Engineering geological surveys are based on information obtained from geological studies. They are supplemented with techniques used in civil engineering investigations such as engineering–geological and hydrogeological mapping, underground exploration, and geophysical, geotechnical, geodetic, and photogrammetric measurements. The basic requirement for an engineering–geological survey is effectiveness. An effective investigation would be insured if the investigation is integrated and carried out in an orderly and prudent fashion. The stages of an engineering–geological survey include reconnaissance investigations, involving an assessment as to whether a proposed structure can be built in the given area; preliminary investigations, involving investigations needed for a basic assessment of engineering–geological conditions with respect to the technical feasibility of the proposed structure; and detailed investigations to provide as complete information as possible about the foundation conditions at the building site. Geological investigations continue during construction, which involve documentation of temporary exposures, correlation of results from preliminary and detailed surveys with actual conditions and, if necessary, conducting control tests.